Prestressed tendon anchor means



Dec. 28, 1965 R. P. MARTTER 3,225,500

PRESTRESSED TENDON ANCHOR MEANS Filed July 17, 1962 Z NVENTOR. RICHARDMAPTTEE se a BY 59 1 1* s5 "4 WM VM ATTORNEVS United States Patent3,225,500 PRESTRESSED TENDON ANCHOR MEANS Richard P. Martter, 1239Highland Ave., Glendale, Calif. Filed July 17, 1962, Ser. No. 210,494 3Claims. (Cl. 52-127) This invention has to do generally with theprestressing of concrete structures.

Concrete bodies, whether columns, beams, floors, pipes or other formsare commonly prestressed by the use of tensioned elongated members, suchas rods or wires, which place a compressive force on the body ofconcrete. Prestressing of the concrete is achieved either bypretensioning or by posttensioning such members. In pretensioning, themembers are tensioned before the concrete is poured and are maintainedin tension by external means until the concrete has reached thenecessary strength and has bonded to the tensioned members. The latterare then released with the reaction transferring to the concrete body.In posttensioning, the wires, which are usually coated and enclosed in aconduit, are placed in the form but not tens-ioned and the concretepoured. When the concrete has cured sufficiently the members aretensioned with the force being transferred to the concrete body throughanchor plates at the ends of the wires. The present application isparticularly concerned with an improved method and means of prestressingby the posttensioning method.

In posttensioning, since the tensioning of the wires takes place afterthe concrete body has been poured it is necessary to have access to theends of the tensioning members. In the case of large floor slabs it hasheretofore been the practice to provide recesses along the edges of theslab to expose the hardware at the ends of each tendon, or group ofwires. This is a costly operation because of the amount of time andlabor involved in constructing the specially shaped forms required tocast the recesses and subsequently required in filling in the recessesto make a flush edge along the slab after the tensioning has beenaccomplished.

An object of the present invention is to provide a novel method andmeans to overcome the disadvantages of the conventional method ofprestressing and a method which enables casting the concrete body in itsultimate configuration thereby greatly reducing the cost of thestructure.

Another object is to provide novel means for anchoring the stressed ortensioned wires including a novel stress washer and arrangement of wirestherein and a novel anchor bar for use therewith.

A further object is to provide a novel stressing bar or anchor bar whichis more eflicient and less subject to failure than the wedge plateswhich are commonly used in conventional construction.

Still another object is to provide a novel tool for use in conjunctionwith a novel form of stressing washer which enables the insertion of ananchor bar after a tendon has been stressed even though the washer isrecessed in the body of concrete and there is only limited working spacetherearound.

Another object is to provide a novel screw anchor having the advantagesof the anchor bar referred to above and a novel tool for use therewithwhich makes it possible to maintain the washer supported against anyreturn movement as the washer is pulled during the stressing operationthereby precluding injury to personnel or damage to the structure asmight occur through failure of the jack or from some other cause.

A further object is to provide a novel screw anchor for use inconjunction with a washer which enables a lift-off reading to be takenconveniently and accurately as may be required.

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These and other objects will be apparent from the drawing and thefollowing description. Referring to the drawing:

FIG. 1 is an isometric view, partially in section, showing one end of atendon and apparatus embodying the invention associated therewithembedded in the edge of a concrete body which is fragmentarily shown insection;

FIG. 2 is a vertical sectional view through the concrete body andapparatus of FIG. 1, together with a tool for stressing the tendon, thelatter being shown stressed;

FIG. 3 is a view in the plane of line 33 of FIG. 2 but showing thecompleted stressed tendon with the anchor bar in position and the voidfilled with grout;

FIG. 4 is a fragmentary sectional elevation on line 44 of FIG. 2, but ona larger scale;

FIG. 5 is a sectional view on line 55 of FIG. 3, but on a larger scale;

FIG. 6 is a view similar to that of FIG. 2, but showing an alternateform of apparatus and showing the parts partially tensioned;

FIG. 7 is a view of the stressed tendon of FIG. 6; and

FIG, 8 is a cross sectional view on line 8-8 of FIG. 7, but on a largerscale.

More particularly describing the invention, referring first to FIGS. 15,numeral 11 designates a concrete body which may be a floor slab, a beam,post or other type of member. This body may be provided with a pluralityof tendons for prestressing it and in FIG. 1, I show one end of a tendondesignated 12 which may be assumed to extend through the body ofconcrete to its edge or end opposite the edge 13 shown in the drawing.As is conventional, the tendon itself is made up of a plurality ofhigh-tensile steel wires 14 and these are anchored at each end in astressing Washer 15, the wires passing through the washer and beingprovided with button heads 16 formed thereon in any suitable manner toanchor the same.

When the wires of the tendon are assembled they are normally coated witha suitable lubricant and wrapped with a fiber-reinforced paper or thelike to provide the sheath 18 shown in the drawings. Thus when theconcrete is cast there will be a void within the sheath. I provide aconventional bearing plate 20 which has holes 21 therethrough to passthe wires. This bearing plate is recessed within the cast body of theconcrete at the time the latter is poured. In order to provide workingspace exteriorly thereof I provide a tubular form or tube 22 which isshown as cylindrical, although it may be of different cross sectionalshape, and this extends from the plate to the outer edge 13 of theconcrete body. It is to be understood that the tendon and connectedparts are located in the forms prior to the pouring of the concrete, andthe tubular form member 22 is preferably attached to the bearing platein order to keep the two parts properly oriented. The member 22 wouldhave its outer end against the inner wall of the main form (not shown)which would define the edge 13 of the concrete body.

It will thus be apparent that a void or space 25 is provided in theconcrete outwardly of the bearing plate but of less cross sectional areathan the plate. This space provide access to the stressing washer 15 sothat a tool may be inserted and attached to the washer for the purposeof tensioning the wires.

In FIG. 2 I show an adapter or tool28 of hollow cylindrical form whichhas an interiorly threaded inner end portion 29 adapted to be threadedonto the washer 15, the latter having a threaded exterior surface forthe purpose. The outer end portion 30 of the tool is solid and providedwith a threaded socket 31 or other type of means for receiving the rod33 of a hydraulic jack 35 such as shown in FIG. 6. With thisconstruction the tool may be threaded onto the washer and the jackoperated to stress the wires 14 by pulling the washer out nearly to theouter edge 13 of the concrete body, as shown in FIG. 2.

One of the features of the invention is the provision of novel means formaintaining the tendon in tension and a novel way of inserting suchmeans. The means comprises a bar 38 which is preferably rectangular incross section and of appropriate length. The upper edge of the washer isrecessed or slotted at 40 to partially receive the bar. Also the tool 28is provided with a slot 42 which is made to register with the slot inthe washer so that the bar may he slipped into the tool and forwardthrough the slot in the washer and thence into final position in thespace between the inner side of the washer and the bearing plate, asshown in FIG. 3. In this connection it should be noted that the wires 14are arranged in the washer so as to provide a space at the top toreceive the bar. This will be apparent from FIGS. 4 and of the drawingwhich shows the pattern of the wires, as being generally U-shaped.

After the bar has been placed in position the jack 35 is removed as wellas the tool 28 and the space or void 25 inside the tubular form 22filled with grout 45 (FIG. 3) or other desired material.

Referring now to FIGS. 6 to 8, I show another form of the inventionwherein the parts are recessed in a concrete body 11 in the same manneras previously described. However, in this form of the invention thewasher, here designated 50, has an internally threaded central opening51 which receives an externally threaded anchor bar or screw 52. Iprovide a tool 55 having an internally threaded inner end portion 56 forattachment to the washer as shown in FIG. 6. This tool has a threadedinner end portion 57 to receive the piston rod or ram 33 of a jack 35which is used to stress the Wires of the tendon.

One of the features of this particular form of the invention is theprovision of a shaft 58 which is slidably and rotatably journaled in acentral section 59 of the tool. The shaft may have a noncircular innerend 60 which seats in a correspondingly shaped socket 61 of the screw 52so the latter can be turned by rotating the shaft. The outer end of theshaft is fitted with a universal joint 63 and a brace 64 extendstherebeyond to facilitate operation.

In the operation of the apparatus, the tool 55 is attached to the washerand the jack operated to pull the washer and attached wires. During thisoperation the brace should be turned to cause the anchor screw to takeup the slack and maintain the washer supported against return movementin event of failure of the jack or other equipment. When the wires havebeen tensioned sufiiciently, the jack and tool are removed and the screwanchor bar 52 serves to maintain the parts in tension. The spaceoutwardly of the bearing plate may be filled with grout 45 to completethe structure, as shown in FIG. 7.

Although I have illustrated and described preferred forms of myinvention, I contemplate that various changes and modifications can bemade therein without departing from the invention, the scope of which isindicated by the following claims.

I claim:

1. In a prestressed concrete body, a tendon comprised of a plurality ofwires extending through the concrete body and terminating short of anouter face thereof;

a bearing plate embedded in the concrete inwardly of said face andextending normal to the direction of the tendon;

a stressing washer on the outer side of said bearing plate, the wires ofthe tendon passing through said plate and being anchored to said washer,said wires being in tension; and

a bar between said washer and said plate;

by maintaining said wires in tension. 2.

est dimension of said bar;

a recess in the side of said washer, the clearance between the bottom ofsaid recess and said void being greater than the smallest dimension ofsaid bar, said recess receiving a portion of said bar while inlongitudinal position permitting said bar to be moved past said washerinto said space after placing said wires in tension.

body and terminating short of an outer face thereof;

a bearing plate embedded in the concrete inwardly of said face andextending normal to the direction of the tendon;

being in tension;

est dimension of an anchor bar;

wires in tension;

a tool having a hollow, internally threaded inner end for threading ontosaid washer, said tool having a slot extending axially from its innerend for a substantial distance and adapted to be aligned to registerwith the recess in said washer, said tool being formed at its outer endfor attachment of a jack, and said anchor bar inserted through said slotand said recess between said washer and said bearing plate when saidtendon has been tensioned by pulling said washer outwardly of saidplate.

References Cited by the Examiner UNITED STATES PATENTS Crisenberry.

RICHARD w. COOKE, JR., Primary Examiner.

JACOB L. NACKENOFF, FRANK L. ABBOTT,

Examiners.

In a prestressed concrete body as defined in claim 1, a void in saidconcrete body extending from said hearing plate to said outer face, theclearance between said washer and said void being less than the small-3. In a prestressed concrete body, a tendon comprised of a plurality ofwires extending through the concrete stressing washer on the outer sideof said bearing plate, the wires of the tendon passing through saidplate and being anchored to said washer, said wires a void in saidconcrete body extending from said bearing plate to said outer face, theclearance between said washer and said void being less than thesmallrecess in the side of said washer, the clearance between the bottomof said recess and said void being greater than the smallest dimensionof said bar, said recess receiving a portion of said bar while inlongitudinal position permitting said bar to be moved past said washerinto said space after placing said Blaton 52-228 Peterson 25429.5

Karig 254--29.5 Birkenmaier et al. 254-295 Middendorf 52-223 Fields etal 52-173 Stubbs 52223

3. IN A PRESTRESSED CONCRETE BODY, A TENDON COMPRISED OF A PLURALITY OF WIRES EXTENDING THROUGH THE CONCRETE BODY AND TERMINATING SHORT OF AN OUTER FACE THEREOF; A BEARING PLATE EMBEDDED IN THE CONCRETE INWARDLY OF SAID FACE AND EXTENDING NORMAL TO THE DIRECTION OF TEH TENDON; A STRESSING WASHER ON THE OUTER SIDE OF SAID BEARING PLATE, THE WIRES OF THE TENDON PASSING THROUGH SAID PLATE AND BEING ANCHORED TO SAID WASHER, SAID WIRES BEING IN TENSION; A VOID IN SAID CONCRETE BODY EXTENDING FROM SAID BEARING PLATE TO SAID OUTER FACE, THE CLEARANCE BETWEEN SAID WASHER AND SAID VOID BEING LESS THAN THE SMALLEST DIMENSION OF AN ANCHOR BAR; A RECESS IN THE SIDE OF SAID WASHER, THE CLEARANCE BETWEEN THE BOTTOM OF SAID RECESS AND SAID VOID BEING GREATER THAN THE SMALLEST DIMENSION OF SAID BAR, SAID RECESS RECEIVING A PORTION OF SAID BAR WHILE IN LONGITUDINAL POSITION PERMITTING SAID BAR TO BE MOVED PAST SAID WASHER INTO SAID SPACE AFTER PLCING SAID WIRES IN TENSION; A TOOL HAVING A HOLLOW, INTERNALLY THREADED INNER END FOR THREADING ONTO SAID WASHER, SAID TOOL HAVING A SLOT EXTENDING AXIALLY FROM ITS INNER END FOR A SUBSTANTIAL DISTANCE AND ADAPTED TO BE ALIGNED TO REGISTER WITH THE RECESS IN SAID WASHER, SAID TOOL BEING FORMED AT ITS OUTER END FOR ATTACHMENT SAID SLOT AND SAID RECESS BETWEEN SAID WASHER AND SAID BEARING SAID RECESS BETWEEN SAID WASHER AND SAID BEARING PLATE WHEN SAID TENDON HAS BEEN TENSIONED BY PULLING SAID WASHEER OUTWARDLY OF SAID PLATE. 